Emerald is a variety of beryl, which is defined by its green color. This coloration results from the presence of chromium and/or vanadium within the beryl structure, and beryls colored green by iron are instead simply known as "green beryl". In addition, the necessity for emeralds to be green means that the terms "pink emerald" (i.e. morganite) and "red beryl" (i.e. bixbite) are misnomers.

The current name is derived from the ancient Greek words for "green gem", but the gem had been mined in Egypt since around 1500 BC. However, the discoveries of emeralds at Muzo and Chivor, in modern-day Colombia, were the most significant in terms of both the quality and quantity of material available to the market.

Emeralds are often of low clarity, and the visibility of the internal fractures is often decreased with the addition of resin-based filling substances.